Page 824 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

Terrestrial Zootoxins Chapter | 58 783

VetBooks.ir capillaries, and tissue necrosis; systemic depletion of clot- been used experimentally. Dapsone can cause methemo-
globinemia as well as hemolysis in individuals with
ting factors (VII, IX, XI, and XII) can also occur (White
glucose-6-phosphate dehydrogenase deficiency (Peterson
et al., 1995; Goddard, 2003; Peterson and McNalley,
2006b). Platelet activation can also be seen (Peterson and and McNalley, 2006b). Antivenins are available for South
McNalley, 2006b). In the presence of calcium and American Loxesceles species. Experimental antivenins for
C-reactive protein, sphingomyelinase D can cause hemo- L. reclusa have been developed. These have been shown
lysis. Finally, lipases can cause free lipids in the blood to be effective if given within 4 h of envenomation.
that may act as inflammatory mediators and/or cause However, these antivenins are not currently commercially
embolization (Peterson and McNalley, 2006b). available (Mullen, 2002b).

Toxicity Hobo Spiders (Tegenaria agrestis)
Dogs injected intravenously with brown recluse venom Background
developed thrombocytopenia, absence of reticulocytes, Hobo spiders are native to Europe but were introduced in
and evidence of hemolysis with decreased hematocrit the Pacific Northwest in the 1930s. They occur mainly in
(Denny et al., 1964). Necropsy showed widespread pete- Washington, Oregon, and Idaho, but their range includes
chial and ecchymotic hemorrhage, dehydration, and hypo- central Utah through western Canada to the Alaskan pan-
cellular bone marrow with depression of the erythroid and handle. In the 1980s, the appearance of necrotic spider
platelet cell lines. Another study (Futrell et al., 1979)of bites in the Pacific Northwest was initially blamed
in vitro hemolysis found that human and pig erythrocytes on L. reclusa, but later the bites were correctly attributed
were far more susceptible to lysis from brown recluse to T. agrestis (Goddard, 2003).
venom than those of dogs. Hobo spiders are poor climbers and build a funnel web
Initially, the bite may produce little pain or local reac- at ground level or in basements. Males will leave their web
tion. Approximately 3 8 h after envenomation, the site at night in search of females and may enter houses while
becomes red, swollen, and tender and forms a “bull’s-eye” doing so. Males are more venomous than females and are
lesion. A vesicle may form and be replaced by a black more likely to bite (Mullen, 2002a,b; Goddard, 2003).
scab or eschar. Tissue around the bite may slough, leaving
a 1- to 25-cm ulcer. Venom distribution may occur in
Toxicity
areas dependent to the bite due to gravity. Healing is slow
In most cases, the bite is initially painless. Within 30 min,
and may take months, often leaving a large scar (Goddard,
a localized expanding area of erythema may occur; the
2003). Diagnosing a brown recluse bite may be difficult if
lesion may eventually reach 15 cm in diameter. Then, in
the bite is not witnessed. In many cases, a brown recluse
approximately 15 35 h, the area ruptures and there is a
bite is “blamed” for necrotic lesions due to other causes
serous discharge from the wound. The wound may require
(Mullen, 2002b). Systemic signs, although uncommon, can
3 years to heal, especially if it is in fatty tissue (Goddard,
be seen with a brown recluse bite; they may develop
2003). In humans, systemic signs may occur in approxi-
48 72 h after exposure. Hemolysis with anemia and
mately 45% of bites, and approximately one-third of these
hematuria, tachycardia, pyrexia, myalgia, vomiting, dys-
may require hospitalization. Signs may include headache
pnea, disseminated intravascular coagulation, and coma
(which can last for days), nausea, weakness, and vision
have been reported but are rare (Goddard, 2003).
changes. The signs may progress to vomiting (often
intractable), watery diarrhea, and bone marrow destruc-
Treatment
tion resulting in anemia, pancytopenia, and thrombocyto-
For the necrotic lesion, local wound care including chemi- penia. Fatalities are rare (Mullen, 2002b).
cal debridement with Burrow’s solution (aluminum ace-
tate) or hydrogen peroxide and bandaging should be Treatment
performed. Pruritus may be controlled with diphenhydra-
Treatment of the hobo spider bite is supportive and
mine (2.2 mg/kg q8h). Antibiotics, especially if infection
symptomatic.
is evident, should be administered. Analgesics for pain
(nonsteroidal antiinflammatory drugs for mild pain and
opioids for severe pain) may be required. Surgical exci- Tarantulas
sion, used in the past, is no longer recommended Tarantulas of the family Theraphosideae are large,
(Peterson and McNalley, 2006b). Dapsone (4,49-diamino- ground-dwelling spiders (Mullen, 2002b). In most cases,
diphenylsulfone) may be helpful in limiting the severity the bite of the tarantula causes little more than localized
of the necrotic lesion because it inhibits neutrophil migra- pain that develops slowly but usually resolves within
tion. In dogs, a dose of 1 mg/kg per day for 14 days has 30 min. Approximately 12 genera of tarantulas that may